Physical and Gas Transport Properties of Novel Hyperbranched Polyimide – Silica Hybrid Membranes

Summary Physical and gas transport properties of novel hyperbranched polyimide – silica hybrid membranes were investigated. Hyperbranched polyamic acid as a precursor was prepared by polycondensation of a triamine monomer, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and a dianhydride monomer, 4,4-(hexafluoro-isopropylidene)diphthalic anhydride (6FDA), and subsequently modified the end groups by 3-aminopropyltrimethoxysilane (APTrMOS). The hyperbranched polyimide – silica hybrid membranes were prepared using the polyamic acid, water, and tetramethoxysilane (TMOS) via a sol-gel technique. 5 % weight-loss temperature and glass transition temperature of the hyperbranched polyimide – silica hybrid membranes determined by TG-DTA measurement considerably increased with increasing silica content, indicating effective cross-linking at polymer – silica interface mediated by APTrMOS moiety. CO₂, O₂, and N₂ permeability coefficients of the hybrid membranes increased with increasing silica content. It was pointed out that the increased gas permeabilities are mainly attributed to increase in the gas solubilities. On the contrary, CH₄ permeability of the hybrid membranes decreased with increasing silica content because of decrease in the CH₄ diffusivity and, as a result, CO₂/CH₄ selectivity of the hybrid membranes remarkably increased. It was concluded that the 6FDA-TAPOB hyperbranched polyimide – silica hybrid membranes have high thermal stability and excellent gas selectivity, and are expected to apply to a high-performance gas separation membrane.     

Fouling Control in a Submerged Flat Sheet Membrane System: Part I – Bubbling and Hydrodynamic Effects

Abstract

Submerged flat sheet membranes are mostly used in membrane bioreactors for wastewater treatment. The major problems for these modules are concentration polarization and subsequent fouling. By using gas‐liquid two‐phase flow, these problems can be ameliorated. This paper describes a study of the use of gas‐liquid two‐phase flow as a fouling control mechanism for submerged flat sheet membrane bioreactors. The effect of various hydrodynamic factors such as airflow rate, nozzle size, intermittent filtration, channel gap width, feed concentration, imposed flux, and the use of membrane baffles were investigated. Experiments conducted on model feeds showed that fouling reduction increased with air flow rate up to a given value and beyond this flowrate no further enhancement was achieved. The effect of bubbling was also found to increase with nozzle size at constant airflow. Using intermittent filtration as an operating strategy was found to be more effective than continuous filtration and it also reduced energy requirements. The study showed the importance of the size of the gap between the submerged flat sheet membranes. As the gap was increased from 7 mm to 14 mm, the fouling became worse and the degree of fouling reduction by two‐phase flow decreased by at least 40% based on suction pressure rise (dTMP/dt). This is the first study which has reported the effects of baffles in improving air distribution across a flat sheet submerged membrane. It was found that baffles could decrease the rate of fouling by at least a factor of 2.0 based on the dTMP/dt data, and significantly increase critical flux.     

Fabrication and Properties of Multilayer Ceramics in the SiC – TiB2 System

The influence of the structure and residual stresses on the strength of multilayer composite ceramic materials in the SiC – MeB₂ system is studied. The composites are produced using slip casting of thin films, stacking and rolling of packets, and hot pressing. The use of β-SiC makes it possible to obtain SiC layers with a porous arch structure reinforced with columnar crystals. The high relaxation capacity of such structures eliminates the formation of cracks in fabrication of the material and provides a high strength. A thermal shock causes progressive local spalling with formation of spit-outs without macroscopic fracture of the material. A pilot process for fabricating multilayer ceramic composites is described.     

Synthesis and Some Properties of a New Compound in the CaO – Al2O3 – ZrO2 System

The phenomenon of heterovalent isomorphism discovered in the CaO – Al₂O₃ – ZrO₂ system yields a compound of a 3CaO · Al₂O₃ · 2ZrO₂ composition at 1450°C in a reducing medium. The effect of various factors on the synthesis of the new compound is described. A roentgenographic characteristic of tricalcium alumodizirconate is presented.     

Synthesis and Properties of Fusion-Cast Refractories in the Al2O3 – B2O3 System

Synthesis and properties of fusion-cast high-alumina refractories in the Al₂O₃ – B₂O₃ system are reported. Adding B₂O₃ is shown to improve density and fabricability of the fusion-cast products. As shown by x-ray diffractometry and petrographic analysis, the phase composition of synthetic products is represented by corundum and 9Al₂O₃ 2B₂O₃ boroaluminate. Corrosion tests in molten industrial glasses have shown the potential use of these materials in the melting technology of VS-92-grade optical lead silicate glass.     

X-Ray Diffractometric Study and Electrophysical Properties of Phases in the CaTa2O6 – NdTa3O9 SYSTEM

The method of x-ray diffraction analysis is used for studying phase formation in the CaTa₂O₆ – NdTa₃O₉ system at up to 1400°C. It is shown that there exists a region of solid solutions of a rhombic crystal system based on NdTa₃O₉, the boundary of homogeneity of which lies at up to 40 mol.% CaTa₂O₆. Specimens of the studied solid solutions possess an elevated dielectric constant (e ～ 50 at room temperature). The temperature dependences of the electrical conductivity and the dielectric constants of the solid solutions in the range 20 – 450°C show that the polarization has a relaxation nature.     

The Effect of Periodic Reactions in the MgO – Al2O3 – SiO2 System on the Phase Composition and Properties of Cordierite-Based Materials

Changes in phase composition and properties of cordierite-based materials depending on the calcination temperature and the calcined talcum/raw talcum ratio in the starting mixture is studied. Periodic features in the behavior of the MgO – Al₂O₃ – SiO₂ system are analyzed in terms of a conjugation scheme of solid-phase reversible chemical reactions. Routes for the spinodal phase decompositions of sapphirine and cordierite solid solutions are proposed. Conditions for formation of a dissipative structure in refractory materials and a specific organization of the phase composition under spinodal decomposition of solid solutions are considered.     

Extended Surfactants Including an Alkoxylated Central Part Intermediate Producing a Gradual Polarity Transition—A Review of the Properties Used in Applications Such as Enhanced Oil Recovery and Polar Oil Solubilization in Microemulsions

The research published in the past half century indicates that surfactant interfacial performance in producing low tension or high solubilization with polar oils is not generally attained with pure conventional species exhibiting well-defined polar and nonpolar parts. The improvement trends reached with surfactant mixtures as well as the introduction of additives like cosurfactants and linkers lead to the introduction of the so-called extended surfactants, whose structure includes an intermediate polarity spacer between the hydrophilic head and the lipophilic tail. Recent investigations on different kinds of surfactants in a variety of applications—such as detergency, cosmetics, enhanced oil recovery or crude demulsifying, and vegetable oil extraction—indicate that these extended surfactants are likely to be particularly performing with oils containing polar groups, such as triacylglycerols and asphaltenic crudes. Possible applications of extended surfactants in enhanced oil recovery, crude emulsion breaking, detergency and cleaning, medicine and cosmetics vehicles, and natural oil extraction as well as some other cases are quickly reviewed.     

Electrical Properties and the Structure of Glasses in the xNa2O–(1 – x)2PbO · B2O3 System

The temperature–concentration dependences of the electrical conductivity and the activation energy for electrical conduction of glasses in the Na₂O–B₂O₃ and Na₂O–2PbO · B₂O₃ systems are studied. The investigation into the nature of the electrical conduction in these glasses reveals that the contribution from the electronic component (10^–3%) of the conductivity is within the sensitivity of the Liang–Wagner technique. A considerable alkali conductivity is observed upon introduction of more than 12 mol % Na₂O. The true transport number of sodium _Na is as large as unity at [Na₂O] 15 mol %. It is shown that the observed temperature–concentration dependences of the electrical and transport properties are governed by the ratio between the concentrations of polar and nonpolar structural–chemical units of the Na⁺[BO_4/2]^–, Na⁺[O^–BO_2/2] Na⁺[O^–BO_2/2], Pb²⁺ _1/2[BO_4/2]^–, Pb²⁺ _1/2[O^–BO_2/2], and [BO_3/2] types.     

Refractory Plastic Masses Based on Highly Concentrated Ceramic Binding Suspensions (HCBS). II. Structural and Mechanical Properties of Plasticized HCBS in the System SiO2 – Clay

Rheological properties of individual suspensions of quartz sand, quartz glass, and Nizhne-Uvel'skoe (NU) clay and compound suspensions of these components containing 20 – 80% NU clay are studied. The effect of NU content on rheological properties of the compound suspensions is considered. Structural and mechanical properties of plastic masses (with a moisture content of 10 – 20%) based on compound suspensions using a Tolstoi plastometer are studied. The data obtained are used to determine the main elastoplastoviscous and structural-mechanical properties of the plastic masses. The effect of the added HCBS on the rheological characteristics is considered.